1. Field of the Invention
The invention relates to method of and to a device for adjusting one or more roll segments in a continuous casting installation for metals, especially for steel materials, the rolls of which are adjusted in the segment upper frame and the segment lower frame on frame cross members by pairs of hydraulic piston-cylinder units in a position-and/or pressure-controlled manner, wherein an operation for guiding and/or pressing the casting strands is switched from a position-controlled to a pressure-controlled operation when the pressure within the respective pair of piston-cylinder units reaches a predetermined maximum value.
2. Description of the Prior Art
In a method for guiding a cast strand with an associated strand guide, the opening width, which corresponds to the thickness of the cast strand, is continuously adjusted during casting so that with a strand guide segment having four piston-cylinder units, two adjacent servo-piston-cylinder units, which are hydraulically combined with each other, are adjusted in accordance with the strand, and the remaining servo-piston-cylinder units are adjusted independently (DE 196 27 336C1).
Proceeding from this known method, WO 99/46 071 discloses the method described at the beginning. However, the known method and strand guides do not encompass all operational processes. In the roll casing, the existing forces are transmitted from the strand guide roll by a roller or slide bearing to a respective frame cross-member. During an operation, which often lasts several days or weeks without an interruption, stresses of different type and magnitude occur. Therefore, operational conditions most often occur which are caused by particularly high loads. Such operational conditions occur during casting at transition from a cold strand head to a hot strand, are caused, during composite casting, by a connection element between the melts of different steel products, and occur when the casting ends, i.e., are caused by strand ends. The strand shape of the transition piece and a ski shape generate particularly high loads. The resulting geometry of a cast strand is transported through the entire casting installation and passes every roll segment which results in different local load conditions. Simultaneously, a continuous strand displacement and suppression of the strand bulging in insured by the ferrostatic pressure. These conditions require particular measures.
The object of the invention is to compensate an overload that occurred previously, by an effective reaction of respective roll segments, i.e., to provide far-reaching protective measures.
The object of the invention is achieved by operating, in the case of overload, the piston-cylinder units of every roll segment in subsequent steps at a reduced pressure or in a pressureless switching mode until the switching mode is reached in which the segment upper frame can be opened to some extent. Thereby, an effective reaction of the roll segments at an increasing load is achieved in response to local load forces, i.e., a controlled reduction of the incoming overload takes place. The segment upper frames with rolls and bearings actively reduce, at the switching xe2x80x9copenxe2x80x9d, the build-up overload.
This regulation possibility is expanded due to the fact that in the pressureless switching condition, the weight of the segment upper frame and friction forces of the relative displacement of the cylinder and the piston of a piston-cylinder unit provide for a locking force.
In order, however, to insure that the xe2x80x9csoftenersxe2x80x9d of the adjusting force would not remain unmeasured, it is proposed to retain a maximum gap between the roll segments and the cast strand at a limited opening of the segment upper frame in the switching mode. Thereby, the set withdrawal or run-in path includes, for all cases, only a small portion of the entire available run-in path. In case this small run-in path is not retained, the strand would bulge in an unpermissible high region at an affected point, and the casting process would not be able to continue.
A device for adjusting one or more roll segment in a continuous casting installation for metals, especially for steel materials, proceeds from a device the rolls of which are adjusted in the segment upper frame and the segment lower frame on frame cross member by pairs of hydraulic piston-cylinder units in a position-and/or pressure-controlled manner, wherein an operation for guiding and/or pressing the casting strands is switched form a position-controlled to a pressure-controlled operation when the pressure within the respective pair of piston-cylinder units reaches a predetermined maximum value. The object of the invention with respect to the device is achieved by providing an adjustable displacement stop in the path of the segment upper frame. Thereby, the segment upper frame is not displaced over the entire possible run-in path.
In order to avoid a need in additional necessary constructional space, it is proposed to arrange the displacement stop between the segment upper frame and the segment lower frame.
According to further features, the displacement stop is advantageously arranged in immediate vicinity of every piston-cylinder unit. With four piston-cylinder units, each piston-cylinder unit includes such a displacement stop.
A displacement stop consisting of a pivoted-in and a pivoted-out toggle lever a pivot axis of which with a first lever arm is supported on the segment lower frame and its second lever arm lies below the segment upper frame in a pivoted-in position, proved itself in practice. The displacement stops are only pivoted in for a casting operation. During maintenance shifts, the displacement stop can be pivoted out, whereby a complete opening and a complete displacement of the segment upper frame can be effected for effecting a maintenance work.
According to other features, the displacement limitation is defined by an abutment mounted on the segment upper frame and forming a predetermined gap.
The gap can be formed by stacking on the abutment of the segment upper frame a plurality of shims for forming a changeable step-by-step gap. For each segment upper frame or for each piston-cylinder unit, the number and thickness of the shims is individually selected. Thereby, it is possible to provide an individual adjustment of a basic set-up of a displacement limitation for each roll segment or for each piston-cylinder unit at the entry side of the cast strand and at the exit side of the cast strand.
A further improvement according to the invention consists in forming the displacement stop simultaneously as an overload protection element, with the toggle lever being provided with a predetermined breaking point. In this way, the roll segment can be additionally protected from extreme overloads (so-called special casting cases).